1. Field of the Invention
The present invention relates to a circuit breaker having a cradle, and particularly, to a circuit breaker having a cradle equipped with a safety device for preventing inner terminals from being exposed to the outside.
2. Background of the Invention
A circuit breaker serves to interrupt an electric circuit upon detection of an abnormal current which has occurred on the electric circuit. For instance, a vacuum circuit breaker is configured to rapidly interrupt an electric circuit by extinguishing an arc generated when the electric circuit is open or closed and when an abnormal current occurs. This vacuum circuit breaker is installed in a distribution board together with other electric devices for driving of a power plant, a substation, an electric motor, etc.
When a withdrawal-type vacuum circuit breaker is accommodated in a distribution board, a breaker body is firstly accommodate in a cradle thus to be connected to a main circuit of the distribution board. When the breaker body is withdrawn from the cradle, the breaker body connected to the main circuit is disconnected from the main circuit.
The vacuum circuit breaker has a ‘driving’ position for supplying a voltage and a current as a power source side terminal and a load side terminal of the breaker body are connected to a power source side terminal and a load side terminal of the cradle, and a ‘test’ position for testing an operation thereof as the power source side terminal and the load side terminal of the breaker body are disconnected from the power source side terminal and the load side terminal of the cradle.
FIG. 1 shows a cradle of a vacuum circuit breaker in accordance with the conventional art. Referring to FIG. 1, the vacuum circuit breaker includes a cradle 1 formed in a hexahedron shape and having an accommodation space 2 for accommodating a breaker body (not shown). The vacuum circuit breaker is provided with a power source side terminal and a load side terminal (not shown) on a rear surface thereof. Under this configuration, the breaker body is inserted into the accommodation space 2 thus to be connected to a main circuit.
The cradle 1 is provided with a shutter for forming a closed space between the terminals of the breaker body and the terminals of the cradle, for stable separation therebetween. This shutter has an upper shutter 3 and a lower shutter 4. Once the circuit breaker is inserted into the cradle for moving to a driving position, the upper shutter 3 and the lower shutter 4 move up and down, respectively. As a result, the shutters form an open space between the terminals of the breaker body and the terminals of the cradle, for connection therebetween.
A shutter opening/closing apparatus 5 for opening and closing the shutter according to movement of the breaker body is provided in the cradle 1. FIG. 2 shows the shutter opening/closing device 5. Referring to FIG. 2, the shutter opening/closing device 5 includes an upper shutter operation link 6a for operating the upper shutter 3 by being connected to the upper shutter 3 and by being rotatably coupled to a pivot 8, and a lower shutter operation link 6b for operating the lower shutter 4 by being connected to the lower shutter 4 and by being rotatably coupled to the pivot 8. The shutter opening/closing device 5 is provided with shutter levers 7a and 7b for driving the upper shutter operation link 6a and the lower shutter operation link 6b by being pressed when the breaker body is inserted into the cradle 1. The upper shutter operation link 6a and the lower shutter operation link 6b are provided with transmission links 9a and 9b connected to the upper shutter 3 and the lower shutter 4, and configured to transmit operations of the upper shutter operation link 6a and the lower shutter operation link 6b to the upper shutter 3 and the lower shutter 4. Under this configuration, the upper shutter 3 and the lower shutter 4 are open and closed.
In the conventional circuit breaker, as the breaker body is inserted into or withdrawn from the cradle, the shutter opening/closing device is driven to open and close the shutter. However, the shutter may be open and closed by a user's arbitrary manipulation. That is, the shutter may be open and closed without any safety device before the breaker body is accommodated in the cradle, or when the breaker body has been separated from the cradle for repair. In this case, if an electric circuit is in a power-on state, an accident may occur.